While I have never been an advocate of overlaying WLAN on a DAS, in theory and some practice this could be done with 802.11/b/g and even (a); however everything comes with a price. Engineering to -85dB for data for 802.11a/g, while not diversity this may or could be done. Adding capabilities for voice (voice over IP), and you have another dimension such as an increased signal strength requirement of -65dBm. Then when you add 802.11a, amplification of the signal is needed either at the antenna element or in the IDF (to meet the link budget. DAS systems work well for what they were intended to do. That is transmitting broadband signals such as traditional cellular at 850MH and PCS at 1900MHz. At these frequencies you have a approximate coverage pattern of 10,780 sq. ft. per antena element. At the VHF or UHF range this dramatically increase to 34,375 sq. ft. However to to meet the link budget requirement when WLAN is combined on a DAS, this decreases coverage to 3,520 ft per antenna element. Adjustments also have to made for 1/2" coaxial cable loss. Going back to 850MHz and 1900MHz, you will have 2.5db of loss for every 100ft at 850MHz and 4.0 db of loss at 1900MHz. At 5.750GHz, this loss increases dramatically to 8.0 db for every 100ft. Now moving to 802.11n and the use of MIMO. The race is on between Verizon and LTE oer 700MHz and Sprint with WIMAX. Not doubt LTE will probably take the edge because of Verizon's major footprint and the fact that a huge build-out is not required as required for WIMAX. DAS companies tend to claim support of 802.11n because of the inherent portended support of MIMO for WIMAX. Again, the question begs to mind how the heck will this work? Oh yes, and how much will this actually cost? Remember MIMO needs multiple antenna pathwyas (in and out x 2). If the AP(s) are in the IDF, will you need four independent runs of coaxial cable or do you extend the AP(s), out on the floor and then come up with a way to run ethernet over coaxial? MIMO should be preserved as it takes advantage of multi-path to increase throughput in theory up to 600MB/sec, realistically 300MB/sec. My suggstion for any enterprise customer that is looking for 802.11n and a DAS is pretty simple. Get a DAS quote for all the broadband services, i.e. cellular, PCS, UHF/VHF, etc. Then get a quote for a discrete (stand alone), WLAN, i.e. 802.11a/b/g/n. Then get a quote from the DAS supplier for broadband services and WLAN services (to include 802.11n). Compare pricing of all quotes two discrete systems versus combined. Finally get in writing as a part of the contract documents that 802.11n will be fully supported in all it's features and functionality. In addition, contact your WLAN provider of 802.11n, and obtain in writing that they have tested and that they approve the use of their specific 802.11n AP and controllers with a DAS.
